A standard modular shelf arrangement includes normally metal ladders that are interconnected with longitudinal beans on which rest metallic panels to form a rigid three-dimensional structure. Such systems are not readily adaptable, with the vertical shelf spacing determined by the vertical spacing of the ladder rungs.
In other known systems molded plastic elements are used that are constituted basically as flat panels with coupling formations in their corners and post parts that can fit between the corners of superposed panels to form the desired three-dimensional structure. While there is no theoretical limit to the height of such an arrangement, it is normally impossible to neatly join adjacent such structures to form a very long shelf; instead adjacent such shelf units are simply formed and fastened together after assembly. Furthermore these arrangement are not normally very robust or very stable.